No push notification received when in standby mode under H3G provider

I bougth this phone two days ago. The android version is 4.4.2 and it is H3G brand (Italy).

When the phone goes in standby, after 10 minutes having locked the screen, it is not able to receive any notification from Gmail or Whatsapp or similar apps... anymore.

When I wake up the phone by unlocking the screen, it receives all the notifications I expected to receive.

I did several trials trying to discover the cause of the problem, and I find out that changing the SIM card (of another provider), the phone works perfectly. So, I went in the shop and asked for a new SIM card, thinking the problem was related to an old SIM card I got.

But this did not solve the problem. I am getting crazy and it was suggested to take the unit for repairing it, but I do not thinks the mobile is damaged...

Hello,
the problem is related only with 3G connection, wi-fi receives all the notifications promptly.
I installed "Push Notification Fixer" app, no root version, and the notifications now are received correctly, unless the ones related to Whatsapp: they continue to keep some short delay (in order of seconds). This is confirmed by the PNF's author as stated in his app description.
There, the reason causing the delay in notification events has been clearly explained, it seems to be related to H3G network connection policies.

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